In the art of high fidelity sound generating systems it has long been recognized that power amplifiers and loudspeaker systems should have a substantially flat frequency response over the desired operating audio spectrum. High grade amplifiers are available commercially which satisfy this criteria and are generally known to have sufficient power and flatness over the spectrum to satisfy the most descriminating requirements. However, the sound transducer system, namely the speaker system, which radiates the audio frequency into the room environment usually does not satisfy the flatness criteria. In a high fidelity sound transducing system, it is not uncommon for the speaker system to cost more than the amplifier and related electronics. Additionally, the perception of sound is not only a function of speaker flatness but also the combination between speaker and room.
It is now well recognized that, unless the sound system is equalized to the room environment, room effects, such as resonant conditions or reflections, can unduly amplify or suppress certain sound frequencies generated by the source in a manner not anticipated by the designer or acceptable to the user.
Prior art systems have attempted to solve the problem of less than perfect amplifiers, less than perfect speaker systems, and less than perfect matching of speaker systems to room environment by applying a test signal to the sound transducer system, including an equalizer, which radiates a band of either white or pink noise into the room. The equalizer in such a system comprises a plurality of contiguous narrow filters covering the entire audio band and an adjustable amplitude control device associated with each filter. There was also provided a microphone whose output was applied to some sort of spectrum analyzer to give a display which is observed by an operator and who can plot frequency versus amplitude curve over the entire audio spectrum. The operator would then adjust each of the amplitude control devices in the system to obtain a flat response over the whole spectrum as observed on the panoramic display device.
The disadvantage of this system is that it requires some spectrum analyzer for adjustment which is very expensive and which has to be brought in for each adjustment or readjustment which is not always convenient. Further, such adjustment requires a skilled artisan that could observe and plot the response curves and make the appropriate adjustment. Finally, there was never any assurance that the filters in the spectrum analyzer were the equivalent of the filters in the equalizer and therefore equalization was often inaccurate.